Basis of Presentation and Summary of Significant Accounting Policies - VIE (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Variable Interest Entity [Line Items]
Total assets	$ 10,364	$ 10,342
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Total assets	287	276
Total liabilities	232	235
Current assets | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Total assets	226	236
Other noncurrent assets | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Total assets	61	40
Other current liabilities | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Total liabilities	215	235
Other noncurrent liabilities | Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Total liabilities	$ 17	$ 0